Lithium transition metal oxide powders and, in particular, lithium cobaltic dioxide having a layered structure, form key cathodic materials for the positive electrode (cathode) in rechargeable lithium ion electrochemical cells.
Specific physical, morphological and chemical characteristics are required to sustain the transition metal oxide's performance over many sequential charge and discharge cycles demanded during service. Current battery applications for the powder demand high purity, homogeneity, controlled particle size and low surface area (less than 2.0 m.sup.2 /g).
Commercial application of the lithiated transition metal oxides, or indeed any cathodic material, is dependant upon the material having a high reversible capacity and conversely a low irreversible capacity, high thermal stability and low cost. Of the three most commonly contemplated compounds, lithium cobaltic dioxide exhibits a high capacity concomitant with a good thermal stability, but it is extremely costly. Lithium nickel dioxide, having a layered structure, possesses high capacity, with low relative cost but is thermally unstable, whereas, lithium manganese oxide (LiMn.sub.2 O.sub.4 having a spinel structure) is the most thermally stable of the three, when delithiated, and is relatively inexpensive but lacks a high capacity. The use of LiNi.sub.j-x Co.sub.x O.sub.2, or indeed transition metal mixed metal oxides in general, is contemplated because of the increased thermal stability thereof in comparison with lithium nickel dioxide and its higher electrical capacity in comparison with lithium cobaltic dioxide. The literature abounds in examples of novel lithium ion systems and variations on the methods for the preparation thereof. In U.S. Pat. No. 4,302,518 issued to J. B. Goodenough et al., lithium cobalt dioxide is prepared by calcining a pelletized mixture of lithium and cobalt carbonates in air at 900.degree. C. for several hours. The calcining step may be repeated one or more times to ensure complete conversion to the desired product. The resultant lithiated cobalt dioxide is characterized in having a hexagonal structure with lattice constants a=0.282 nm and c=1.408 nm as described by T. Ohzuku et al. (J. Electrochem. Soc. 141, 2972, 1994). Reaction parameters will determine lattice structures. Thus, as disclosed in Solid State Ionics, 53-56,681 (1992) by R. J. Gummow et al.,and U.S. Pat. No. 5,160,712 issued to M. M. Thackeray et al., lithium cobalt dioxide prepared by the reaction of lithium and cobalt carbonates in air at 400.degree. C. for between 2 to 5 days yields a product having a cubic structure having the lattice constant a=0.28297 nm (c/a=4.90). The '518 patent further teaches a process for the preparation of lithium nickel dioxide by reacting lithium hydroxide with nickel powder involving multiple regrinding and calcining stages.
In U.S. Pat. No. 4,980,080 issued to A. Lecerf et al., there is described a process for the synthesis of Li.sub.y Ni.sub.2-y O.sub.2 or LiNi.sub.1-x Co.sub.x O.sub.2. To prepare the LiNi.sub.1-x Co.sub.x O.sub.2 compound, a physical mixture of hydrated lithium hydroxide and nickel and cobalt oxides are heated in air at a temperature in the range of about 700.degree. C. A reheating step is then undertaken to complete the solid state reaction.
U. von Sacken, in U.S. Pat. No. 5,180,574 discloses a synthetic pathway for the production of lithium nickel dioxide which comprised reacting nickel hydroxide, nickel oxides, or a mixture thereof, with a 25% stoichiometric excess of lithium hydroxide at 600.degree. C. in an atmosphere substantially free of carbon dioxide.
The present Assignees, in a pending application Ser. No. 08/510,421, the disclosure of which is incorporated herein by reference, described a process for the synthesis of lithium cobalt dioxide and lithium nickel dioxide.